81 gs650gl weak spark

[rafael garza]

I am getting a really weak spark at the spark plug. I picked up the bike for free and need some help getting it started. Where should i start? I have already replaced the spark plugs.

[spyug]

How do you know you have a weak spark? Even a really weak spark will fire if compression is good and the air fuel mixture is right. Can you tell us what you have done to check and what you are seeing? Is every lead weak or are two leads sparking more than the other two? Firing problems are or can be a combination of issues i.e.spark and or lack of fuel and or compression. Do you know you are getting fuel to the cylinders? With bikes that have sat for a while the carbs and or petcock may not function correctly and no fuel is getting in. No amount of spark will fire without fuel.

If it is a low spark problem, everything starts at the battery. You need to know that you have a fully charged battery and good grounds in your wiring. Charge the battery on a 1or 2 amp trickle charge and see what the maximum charge is when measured across the poles ( after 5 or 6 hours of charging). It needs to be high 12s low 13s. Anything as low as 12.5v or lower and your going to have problems. These bikes do not like to fire with anything less than about 12.5 volts.

Clean off your battery terminals and especially the cable from negative side of the battery to the frame or at the engine grounding point. You need good metal to metal attachments. Also locate your TCI (spark controller) box and pull and clean all connectors. Most electrical issuses are as a result of poor/corroded connectors. As the starter circuitry runs through the right hand control module ( i.e. the starter button) disassemble this and clean all connections.

Coils can be a problem but usually infrequently. They will take a lot of punishment before letting go and its usually one at a time. Plug leads can also go bad but it is usually a one at a time thing also.

Give us more detail and we can get deeper into a diagnosis with you.

Cheers,
Spyug.

[doctorgonzo]

I am getting a really weak spark at the spark plug. I picked up the bike for free and need some help getting it started. Where should i start? I have already replaced the spark plugs.

Work backwards from there. Are the plug wires old, cracked.... mine were. The problem is on these old bikes is that the plug wires are attached to the coil so you can't replace just the wires (though I think it can be successfully done if you're lucky and know what you're doing. I say lucky because sometimes you can get them off the coil without trashing it and sometimes no). My solution was a higher output aftermarket set of coils with replaceable wires.

[rafael garza]

Thanks alot for the responses. Well the spark is the same on all four plugs. i've changed out a ground wire because it was burned up.i'm going to check the wires from the coils thru out the bike i have a manuel so im going to give it my best shot. thank again.

[andrewclaycomb]

Go through and cleanup/redo any grounds that look suspect. On my bike I ran a few grounds directly from the battery.

There's a link on here for the coil relay mod and it works really well because it bypasses a lot of your old wiring harness and provides power almost directly from the battery.